Fix almost every warning (#2195)

Fix almost every warning as of Clang 19

* <codecvt> is deprecated, we can use QString's UTF-16 conversion
  instead
* remove sem_timedwait implementation as we don't need it anymore
* remove a useless shift that has its result discarded
* change usages of deprecated sprintf to snprintf

src/frontend/qt_sdl/MPSettingsDialog.h

@@ -54,7 +54,7 @@ public:
     }
 
 private slots:
-    void done(int r);
+    void done(int r) override;
 
     //